1. Field of the Art
The present invetion relates generally to a method of manufacturing an electrochemical cell, and more particularly to an improved method of manufacturing electrochemical cells with an improved consistency in quality, which use solid electrolyte for determining or measuring the concentration of a component of a gas.
2. Related Art Statement
There have been known various electrochemical devices, each of which comprises at least one electrochemical cell using a solid electrolyte body. Such electrochemical devices are used, for example, as oxygen sensors to detect the oxygen concentration of an exhaust gas from internal combustion engines of automotive vehicles. Typical examples of such oxygen sensors include an oxygen sensor which employs a mass of oxygen-ion conductive solid electrolyte such as zirconia ceramics, to determine the oxygen concentration according to the principle of an oxygen concentration cell. Also known in the art are electrochemical devices or elements which are used as sensors or detectors for hydrogen, nitrogen, carbon dioxide, etc. In the field of producing such electrochemical devices, there has been an increasing trend of using an electrochemical cell of laminar structure which comprises a planar solid electrolyte body and planar electrodes disposed in contact with a surface or surfaces of the planar body of solid electrolyte.
In the production of such electrochemical cells, a diffusion layer having a predetermined diffusion resistance to molecules of a measurement gas is formed on a body of zirconia ceramics or other solid electrolyte so as to cover an electrode which is disposed on the solid electrolyte body for exposure to an external measurement gas, so that the atmosphere contacting the electrode is controlled by the diffusion layer covering the electrode. It is also known that a pair of electrodes are disposed on opposite sides of such a diffusion layer so that the diffusion layer functions as a solid electrolyte body through which the pumping current flows by application of a pumping current to the two electrodes. In either case, the electrochemical cell for determining the concentration of a given component of a measurement gas, comprises a solid electrolyte body, and at least one pair of electrodes which are disposed on the solid electrolyte body and spaced apart from each other, such that at least one of the pair of electrodes is exposed to the measurement gas via a porous ceramic diffusion layer having a predetermined diffusion resistance to molecules of the component of the measurement gas, so that the atmosphere adjacent to the above-identified at least one electrode is controlled by means of reaction at the at least one pair of electrodes by application of an electric current thereto.
The porous ceramic diffusion layer of the electrochemical cell indicated above may be formed, for example, by firing an unfired or calcined layer of suitable material, together with unfired or calcined layers of other members of the electrochemical cell, so that a laminar structure including the porous ceramic diffusion layer is co-fired. Alternatively, the porous ceramic diffusion layer may be formed by melting spinel or similar material by a plasma flame and spraying the molten material on the layer of the solid electrolyte.